1. Field of the Invention
The invention pertains to the field of latch mechanisms that facilitate online replacement of printed circuit board cards, and more specifically, to latch mechanisms that also function as switches that provide signals facilitating replacement of the printed circuit boards while associated electronic systems remain active.
2. Discussion of the Related Art
Computer system maintenance, repair and upgrade operations sometimes involve the insertion or replacement of printed circuit boards. Standard operating procedures for the insertion or replacement of expansion cards have traditionally required the computer system to be shut-down or powered off during the insertion or replacement procedures. This requirement is problematic because the computer system is unavailable to fulfill its intended function during the procedure. The system unavailability is not necessarily a problem in some cases; however, unavailability causes severe disruptions in other cases. For example, in the case of a telecommunications server that supports a large number of clients, even temporary unavailability of the server may cause extreme inconvenience to the client base.
One solution to the problem of having to shut down computer systems for maintenance is to provide an online or hot-swapping capability that permits the insertion and removal of expansion cards while the system is operational. For example, U.S. Pat. No. 5,568,610 teaches the use of capacitive plates coupled to corresponding variable frequency oscillators that, in combination, detect the insertion or removal of an expansion card. This solution, as well as other solutions involving closely aligned pins in the printed circuit board and the bus into which it is inserted, require that close alignments be made in order to provide a signal to the system indicating that the printed circuit board is being removed. False signals can be created by slight misalignments, and there is often insufficient time to complete a graceful shutdown of the printed circuit board if the printed circuit board is removed too quickly.
There exists a present need for a mechanically and electronically reliable latch mechanism that is capable of signaling a system during the online replacement of printed circuit boards.
The present invention overcomes the problems that are outlined above by providing an improved latch mechanism having mechanically and electronically reliable features for use in signaling a system during the online replacement of printed circuit boards.
The ejector latch mechanism may be used in detachable mounting of a printed circuit board in a bus on a chassis for an active system. The printed circuit board includes a corner, an edge forming part of the corner along a width dimension of the printed circuit board, a switch component proximate the edge, and a latch pin that is located at a position removed from the corner proximate the edge. A pivotable latch body is mounted to the printed circuit board proximate the corner through use of a hinge pin. The latch body includes a first end having cooperable structure for interacting with the switch component to signal pivotal movement of the first end. A second end of the latch body has structure for interengagement with the chassis, such as an arm extending to a greater width than does the edge of the printed circuit board, that selectively locks the latch body in a closed position against the chassis and unlocks the latch body by pivotal motion of the latch body into an open position away from the chassis. A hook is pivotally mounted to the latch body for selective engagement against the latch pin when the latch body is in the closed position.
Special aspects of the hook may optionally include a spring that biases the hook into engagement with the latch pin. The spring may be integrally formed with the hook.
The second end of the latch body may be provided with a ledge that is positioned to contact the chassis upon pivotal motion of the latch body into the open position. The ledge, by virtue of this contact against the chassis, is operable for pulling the printed circuit board out of the bus commensurate with the pivotal motion of the latch body into the open position.
In operation, the system is configured for interpreting a signal from the switch component indicating whether the cooperable structure for interacting with the switch component on the first end of the latch body is interacting with the switch component. The signal provides an indicator that the latch body is in at least one of the closed position and the open position. The system is configured for interpreting the signal from the switch component and causing a graceful shutdown of the printed circuit board commensurate with pivotal movement of the latch body into the open position. The signal changes with closure of the latch mechanism following replacement of the printed circuit board. The system interprets this signal, as appropriate, and restores the printed circuit board to an active operational state commensurate with pivotal movement of the latch body into the closed position. FIG. 5 is a midsectional view taken along line 5xe2x80x945 of FIG. 2.